The development of complementary metal-oxide semiconductor (CMOS) integrated circuits is notable for aggressive scaling of device dimensions and threshold voltage. Gate oxide thickness is also scaled to increase channel conductivity and performance when a CMOS field effect transistor (FET) is in active mode (i.e., switching output). However, at very small thickness levels, electrons can tunnel through the thin gate oxide when the FET is in active standby mode (i.e., static output). The resulting gate leakage current (lot) from the gate to the body (also known as bulk or substrate) as gate oxide thicknesses are increasingly scaled contributes to overall integrated circuit power consumption.
In some driver circuits, the output is held low by coupling the output to ground (GND) through an activated pull-down FET or held high by coupling the output to a supply voltage (VCC) through an activated pull-up FET. The pull-down FET is typically activated by providing VCC to a gate of the pull-down FET and the pull-up FET is typically activated by providing GND to a gate of the pull-up FET. The gate voltage may typically be VCC or GND, and results in gate leakage current (IGB). Moreover, a pre-driver circuit may be used to drive the gates of the driver circuits. Transistors of the pre-driver circuit may also have gate leakage current (IGB) contributing further to overall integrated circuit power consumption.
An approach that has been taken to reduce IGB in the transistors of the driver circuit is to use thicker oxide transistors which are more resistant to gate bias induced IGB. A disadvantage of this approach, however, is that the transistors having thicker gate oxides may be less responsive during switching of the output signal. That is, the speed at which the thicker oxide transistors respond to input signals is comparatively slower than thinner gate oxide transistors, which in systems where high-speed switching is desirable may be unacceptable.
Accordingly, it is desirable for alternative circuits and methods for reducing IGB in driver circuits, which in turn, may reduce power consumption.